The Pentagon chief says the US and its allies are still trying to figure out details of Syria's suspected use of chemical weapons against its own people.
Defense Secretary Chuck Hagel says US and allied intelligence agencies are "continuing to assess what happened, when, where and so on."
The Obama administration said last week that U.S. intelligence had concluded that Syrian government forces been.
Britain, France and Israel also believe chemical weapons have been used in Syria's likely used chemical agents against rebels in two attacks, but said there were "varying degrees of confidence" about how large an attack it may have two-year-old civil war.
President Barack Obama has said such use would bring "enormous consequences" for the Syrian regime.
